Giant Impact Near India — Not Mexico — May Have Killed Dinosaurs

byNancy AtkinsononOctober 19, 2009

Three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-tick Cenozoic strata and water column were removed to show the morphology of the crater.

A huge, mysterious basin off the coast of India could be the largest, multi-ringed impact crater ever found on Earth. And if a new study is right, this impact may supercede the one that created the Chicxulub crater off Mexico’s Yucatán Peninsula as what may have been responsible for killing the dinosaurs 65 million years ago. Sankar Chatterjee of Texas Tech University and a team of researchers have been studying a 500-kilometer-wide (300-mile-wide) depression on the Indian Ocean seafloor which was likely created by a bolide perhaps 40 kilometers (25 miles) in diameter. Such an event would have triggered worldwide climate changes, including intensified volcanism, that led to mass extinction.
Since the 1990’s the leading candidate for what killed the dinosaurs was a ten-kilometer-wide (six-mile-wide) asteroid thought to have carved out the Chicxulub crater. This impact may have done the job, but if not, 300,000 later the impact that created the Shiva basin surely would have finished off large life on Earth.

The massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources. Some complex craters are among the most productive hydrocarbon sites on the planet.

“If we are right, this is the largest crater known on our planet,” Chatterjee said. “A bolide of this size, creates its own tectonics.”

However, some geologists have disputed whether the Shiva depression was created by an impact, or if it is just a hole in Earth’s crust, possibly created by volcanism. Christian Koeberl, a geochemist at the University of Vienna in Austria, has been adamant in the past that Shiva is not an impact crater. He said not only is there no evidence of impact in the case of Shiva, there is no crater structure. He calls Shiva, “a figment of imagination.”

“There’s not even ambiguous evidence, or inconclusive evidence,” says Koeberl. “There are a couple of people that keep pushing for some crater in the Indian Ocean, but this is inconsistent not only with the regional geology and geophysics, but also with anything we know about impact cratering.”

But Chatterjee feels sure that Shiva is an impact crater and said the geological evidence is dramatic. Shiva’s outer rim forms a rough, faulted ring some 500 kilometers in diameter, encircling the central peak, known as the Bombay High, which would be 3 miles tall from the ocean floor (about the height of Mount McKinley). Most of the crater lies submerged on India’s continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India.

If the huge depression was created by an impact, Earth’s crust at the point of collision would have been vaporized, leaving nothing but ultra-hot mantle material to well up in its place. It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions that covered much of western India. What’s more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.

The team hopes to go India later this year to examine rocks drill from the center of the putative crater for clues that would prove the strange basin was formed by a gigantic impact.

“Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly,” Chatterjee said. Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact.

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If an object, sized 40km and leaving a crater 500km wide, hits the earth, is it capable of disrupting or altering the traject of the earth around the sun?
Is it possible that climate changes happened back then not only because of the dust in the air, but because of a changed orbital path?

@silenius: Nowhere near enough to matter. Even if you assume an object like Asteroid Ida hitting the earth at 100km/sec, and it all turns into kinetic energy delivered directly into the planet, you’re looking at less than a ten-millionth of Earth’s orbital kinetic energy. A quick look at wikipedia’s Orders of Magnitude (Energy) article … Hmm, imagine you’re drifting through space at 5 m/s, and I try to alter your trajectory by having a bee hit you with its wing. That’s about the scale of relative energy. Yes, trajectory altered, but it pales in comparison to everything else going on at the same time.

Would this have changed the orbit of the Earth? A bit, but not much. The impactor with mass m and velocity v impacts the Earth with mass M and velocity V. The Earth after impact has a mass M + m and a velocity U. So apply conservation of momentum

mV + mv = (M+m)U.

To make this easy we consider this in the frame of the Earth at the impact, so V = 0. The change in the velocity of the Earth is then U which is

U = mv/(M+m) ~ (m/M)U.

The mass is all we need to figure out. We assume approximately the same densities for the mass of the Earth and the bolide. The volume 4pi/3R^3 of the two now is all we need to consider. So the ratio of the radii of the two is r/R = 40/6400 = 0.000625 and the ratio of the cube of these gives the ratio of the masses ~ 2.44e^-10. So if we assume the bolide impacted at ~ 20km/sec then the change in velocity is 4.9e-9km/sec or about 4.9e-3mm/sec. That is not a whole lot.

Hmmm – we have one group that are adamant that there IS an impact crater, with the evidence being ‘dramatic’, and one group that claims that there is zero evidence, even suggestive, and that it is a figment of imagination.

Somebody will eventually have to pull a massive about-face when the evidence (or lack of) comes in.

A quick research for me brought up the possibility of the “multiple impact theory”. This thought hit my feeble brain as soon as I read the article. Remember dear Shoemaker-Levy 9 and the damage done to the surface of Jupiter, plus the time it took for that to clear up on a gaseous surface. Multiple-shock from two or mor large to gigantic hits within a short timeframe could well have accounted for the damages done back then.??

(Pardon my poor spelling in a place or two,) I meant to be certain to insert the word “here” at the end between “damages done” and “back then”, as in, when multiple strikes to Earth would be a likely culprit to the loss of dinosaurs et. al. (think I better get some sleep before head hits the screen!)

Regardless of what the scientific community findings on which ‘rock’ was the greater cause of the dinos’ demise, I would hate any of those 2 ‘rocks’ to hit Earth today because we will have a very bad day!!!!!

“Regardless of what the scientific community findings on which ‘rock’ was the greater cause of the dinos’ demise, I would hate any of those 2 ‘rocks’ to hit Earth today because we will have a very bad day!!!!!”

The article does mention a future expedition to the area that will search for shocked quartz, among other things. This question about shocked quartz also came to mind as I read the article. Seeing none has even been found to date makes me wonder if this hypothesis is a little premature.